(1) Field of the Invention
The present invention relates to fuel cells, and more specifically to a novel fuel system designed for use with a solid oxide fuel cell for powering unmanned underwater vehicles.
(2) Description of the Prior Art
The most logical choice of an energy source for an unmanned underwater vehicle would appear to be a battery, since it can be operated in the absence of air. However, most batteries lack sufficient energy density to carry out the long missions associated with unmanned undersea vehicles, and the few batteries that might find application, for example lithium thionyl chloride, are prohibitively expensive. There continues to be a need for energy sources with a high energy density that can power unmanned undersea vehicles. These energy sources need to have long endurance, quiet operation, be relatively inexpensive, environmentally friendly, safe to operate, reusable, capable of a long shelf life and not prone to spontaneous chemical or electrochemical discharge.
In an effort to develop power sources for unmanned undersea vehicles with increased energy density, research has been directed towards semi fuel cells and fuel cells as one of several high energy density power sources being considered. For larger scale unmanned underwater vehicles, and longer duration missions, proton exchange membrane fuel cells and solid oxide fuel cells are being used because they can be completely re-fueled from both a fuel and oxidizer standpoint.
A key requirement for an unmanned underwater vehicle powered by a solid oxide fuel cell and maneuvering in shallow water in a surveillance mode is that its presence goes undetected. Stealthy operation of the unmanned underwater vehicle will depend, in part, on the reduction or elimination of any “signature” caused by the evolution of the product gas carbon dioxide, CO2. Carbon dioxide, produced from the use of hydrocarbons in a solid oxide fuel cell must be contained and stored onboard the unmanned underwater vehicle. Since proton exchange fuel cells require pure hydrogen, H2, for their operation, and release only water, H2O, as a product, carbon dioxide is not an issue. However, proton exchange membrane fuel cells cannot run on hydrocarbon fuels because their platinum-metal catalysts will not tolerate any carbon monoxide, CO, that forms inside the fuel cell. For this reason, what is needed is a solid oxide fuel cell fuel system that offers an innovative solution to address carbon dioxide evolution.